Design Of X-Band Low Phase Noise Voltage Control Oscillator

As an important part of transmitter and receiver in communication equipment,microwave oscillator's quality determines the amount of noise introduced into system.Therefore,the design of low phase noise VCO plays a crucial role in improving the performance of the transceiver system.This paper mainly studies and designs X-band Low Phase noise VCO.Based on the formula,this paper studied and analyzed the key factors affecting the phase noise of VCO,which include the selection of transistors and its working area,the Q₀ of resonator,and the Q_eof resonator coupled with external circuit.In order to design a VCO with low phase noise,a suspended microstrip resonator with high Q value is designed,its basic principle and characteristics are introduced,and the concepts of Q and coupling coefficient of the resonator are described.At the center frequency of 8.7GHz,half wavelength open suspended stripline and ring-shaped suspended stripline resonator with different coupling degree are designed respectively,and the S-parameter curve is obtained by simulation.The influence of coupling degree on the Q_L is verified by the formula of on Q_L.Then the main structure and index of the oscillator are introduced,and the main advantages and disadvantages of the oscillators with different structures are analyzed.Using the principle of negative resistance to design a5.8GHz oscillator,the paper achieved two oscillators composed of lumped component and distributed component.The test results are basically consistent with the simulation results,indicating that the spice model of BFP640 is accurate.Based on the above results,the VCO with series and parallel feedback structure is studied and designed respectively.By using ADS and HFSS joint simulation and optimal design,a low phase noise oscillator at 8.7GHz was obtained.The VCO with a certain tuning bandwidth is designed by adding varactor diode.At the end of the paper,the designed VCO has been processed and tested.Through debugging,the designed requirements were achieved.The measured x-band series feedback VCO oscillation frequency point is 8.716GHz,with the tuning bandwidth of 262.1MHz.The output power is 7.57d Bm,and the second harmonic suppression degree is 14.57d Bc/Hz.The phase noise is-86.84d Bc/Hz@10KHz,-109.31d Bc/Hz@100KHz,-132.59d Bc/Hz@1MHz.The measured x-band parallel feedback VCO has an oscillation frequency of 8.656GHz,a tuning bandwidth of 108MHz,an output power of 1.29 d Bm and a phase noise of-92.83d Bc/Hz@10KHz,-114.03d Bc/Hz@100KHz,-142.00d Bc/Hz@1MHz.